Hi All.....Firstly thanks for the add....I am replacing the radiator in my D4 7U Serial No.7U38454 & was wondering should I put inhibitor in it....if so at what ratio & how much water the radiator & block hold...Thanks for any help & advice

About eleven gallons. Use 50/50 mixture of water and anti-freeze and two quart of inhibitor.

It's best to use distilled water. The distilled water doesn't have mineral content which contributes to rust.
Craig 

if you havent got distilled water. rain water or water run through a reverse osmosis unit is just fine. most distilled or deionised water is made by using a ro system anyway. with ionexchange post filtration to make it deionised.most auto parts joints and cleaning supplies will have large quantities of deionised or distilled water ie 5 gallon drums.

it holds 11 us gallons approximately

what i use in ours is a product called ecocool aoc1000 from australian organic coolants. at a 7.5 percent ratio. it has a life of 6 years or 12,000hrs.
we also use it in the ute and our other machinery too.

www.aoc.net.au/pdf/aoc1000/AOC%20-%20Pro...in%20-%20AOC1000.pdf

I have a dumb question about this topic. I have read lots of discussions on other forums about the critical need to use specific types of anti-freeze for modern diesels, to prevent cavitation and erosion of the cylinder liners. Is that at all relevant to our old Cat diesel engines, or will plain old green Prestone type antifreezes be adequate?

depends where you are. but its more the corrosion inhibiting than anti boil/ anti freeze. if your some where that gets freezing temps then you need anti freeze as well as the corrosion protection.
for my area we don't get that cold so anti boil is more important.
the big thing is that whatever product you use is suitable for engines with copper, brass and cast iron/steel components. and dont mix different types of coolants. and COLOUR MEANS NOTHING that just so happens to be the dye the manufacturer chose. you need to read the specification table/product data sheet. it should say something along the line of atsm type xyz etc